Various configurations of disk brakes have been in large volume production for many years. Disk brakes have been useful because they provide advantages such as excellent heat dissipation and light weight in comparison with the braking load. In the case of aircraft brakes, the braking loads from large jet aircraft are extremely high and have required manufacturers to continually press the state of the art in order to deal with the tremendous heat loads experienced particularly upon landing. One response has been to go to carbon composite materials as disclosed in the Ely U.S. Pat. No. 3,731,769 and in Yoshida U.S. Pat. No. 5,306,078. Another problem resulting from the heat generated in aircraft brakes has been warping of the rotors. One approach to dealing with this problem is disclosed in the Holcomb U.S. Pat. No. 3,456,768 which teaches segmented disk elements with laminated sections.
The requirements for materials used in disk brakes are several, some of which are as follows:
1. High conductive thermal coefficient to transfer thermal energy; PA1 2. High friction coefficient; PA1 3. High metal strength to prevent distortion and breaking; PA1 4. Low weight; and PA1 5. Minimizing of metal galling, especially at high temperatures.
Preferably, all of the above should be accomplished within the framework of low to reasonable production costs and therefore, low selling price.
The kinetic energy absorbed in a vehicle disk brake is equivalent to the total kinetic energy of the vehicle it is stopping, divided by the number of disks. This kinetic energy is converted into heat and has to be rejected to the mounting structure of the wheel and to the surrounding atmosphere.
The two most common processes used in the manufacture of complete (non-segmented) rotors for disk brakes are casting and/or machining from billets of solid metal. These methods are limited to cast iron, steel alloys or aluminum alloys. Metal castings tend to be crude and must be heavy to provide the required heat dissipation and strength at high temperatures. Casting makes it possible to incorporate cooling fins. However, the casting process is limited in the amount of internal cooling fins that can be produced. Cast material physical properties are usually low.
Machining from a solid billet of material produces a lighter disk rotor than can be achieved by casting. It is not possible, however, to provide the needed internal fins that aid cooling and such rotors are therefore susceptible to failure from heat.
Some aircraft and race car applications use solid graphite disks with holes drilled axially to create the desired air passages. The thermal surface available for cooling in these disks is limited. These graphite disks need to work at very high temperatures to achieve the necessary friction coefficient. This can lead to overheating and failure of the other brake components.
In really severe service such as landing loads of large aircraft and with racing cars, the heating loads are such that the brakes are frequently short lived and failures are not uncommon. There is therefore a continuing need for improved disk brakes, and, more particularly, for improved rotor constructions capable of dissipating heat more effectively than rotor designs presently available.